Leadless implantable medical device with fixation antenna member

ABSTRACT

Devices and methods are provided for a leadless implantable medical device (LIMD) comprising a housing. An electrode is disposed on the housing. An electronics circuit is disposed in the housing and is configured to sense cardiac signals, and/or generate and deliver pacing signals to the electrode. A transceiver circuit is disposed in the housing, and is configured to communicate wirelessly with an external device. A fixation antenna electrically separate from the electrode is disposed on a distal portion of the housing and is electrically coupled to the transceiver circuit, and configured to operate as an antenna for communication between the transceiver circuit and the external device.

REFERENCE TO RELATED APPLICATIONS

The present application represents a divisional application of, andclaims priority to, U.S. application Ser. No. 15/661,916, Titled“LEADLESS IMPLANTABLE MEDICAL DEVICE WITH FIXATION ANTENNA MEMBER” whichwas filed on Jul. 27, 2017, the complete subject matter of which isexpressly incorporated herein by reference in its entirety.

BACKGROUND

Embodiments herein generally relate to implantable medical devices andmore particularly, to a leadless cardiac pacemaker with a combinedfixation antenna member.

An implantable medical device (IMD) is a medical device that isimplanted in a patient to, among other things, monitor electricalactivity of a heart, and optionally to deliver therapy, such as acardiac pacemaker. For cardiac applications, pacemakers are used todeliver pacing pulses to a cardiac chamber to induce a depolarization ofthat chamber, which is followed by mechanical contraction of thatchamber, when a patient's own intrinsic rhythm fails. The IMD furtherincludes sensing circuits that sense electrical activity for thedetection of intrinsic cardiac events such as intrinsic atrialdepolarizations (detectable as P waves) and intrinsic ventriculardepolarizations (detectable as R waves). By monitoring electricalactivity, the IMD is able to determine the intrinsic rhythm of the heartand provide stimulation pacing pulses that force atrial and/orventricular depolarizations at appropriate times in the cardiac cycle tohelp stabilize the electrical rhythm of the heart.

Some known IMDs utilize one or more electrically-conductive leads thatextend from a remotely-located canister or pulse-generator and traverseblood vessels and cardiac chambers to affix connected electrodes to theheart. The housing or canister, referred to as a “can”, has electronicsand a power source. The can, including the power and processingcircuitry, and a portion of the leads are located outside of thepatient's heart, and the power and data signals are relayed to and fromthe heart via the leads. However, the presence of leads may beassociated with and/or cause a number of complications.

To mitigate the limitations and complications associated withtransvenous leads and the associated IMD, smaller sized devicesconfigured for intra-cardiac implant without the need for transvenousleads have been proposed. These leadless implantable medical devices(LIMD), such as a leadless cardiac pacemaker, are devoid of leads thatpass out of the heart to another component, such as a can locatedoutside of the heart. The entire device is configured to be attached tothe heart with a fixation antenna, such as a helical member that screwsinto endocardial tissue. Thus, the power source and the processingcircuitry are contained within the device that is attached to the heart.The LIMD includes electrodes that are affixed directly to the can of thedevice, instead of being separated by a distance traversed by one ormore leads. Each LIMD is capable of local pacing and sensing in thechamber of the heart where it is implanted.

Some IMDs communicate with external devices and/or other implanteddevices through a radio frequency (RF) antenna. However, the small sizeof LIMDs create challenges when designing antenna to satisfy the sizelimitations to fit within the device. Placing an antenna on the exteriorof an LIMD also presents challenges. For example, conventional assemblyprocesses for IMDs do not readily permit the addition of externalantenna due to an increase in cost and/or assembly time. In addition, anexternal antenna on the device can interfere with the fixation antenna'sability to hold the LIMD in place.

SUMMARY

In accordance with an embodiment, a leadless implantable medical deviceis provided comprising a housing. Anelectrode is disposed on thehousing. An electronics circuit is disposed in the housing andconfigured to sense cardiac signals from the electrode and/or generateand deliver pacing signals to the electrode. A transceiver circuit isdisposed in the housing and configured to communicate wirelessly with anexternal device. A fixation antenna is electrically separate from theelectrode and disposed on a distal portion of the housing. The fixationantenna is electrically coupled to the transceiver circuit andconfigured to operate as an antenna for communication between thetransceiver circuit and the external device.

Optionally, the housing includes a feedthrough and the fixation antennaincludes a proximal end connected through the feedthrough to thetransceiver circuit. The fixation antenna includes a distal end that iselectrically open. The fixation antenna is configured to operate as amonopole antenna for communication between the transceiver circuit andthe external device. The fixation antenna includes a body that extendsbetween the proximal and distal ends, the body having a length definedbased on a wavelength of a carrier frequency for communication with theexternal device. The length of the body is a quarter multiple of thewavelength of the carrier frequency. The fixation antenna are configuredto communicate in accordance with at least one of a MICS protocol, a BLEprotocol, a WiFi protocol, or a Bluetooth protocol. The housing iselongated and extends along a longitudinal axis, the fixation antenna iswound in a helix about the longitudinal axis, the fixation antennaformed of a material having a deflection DEF=LEN_(REST)/LEN_(EXTEND)that is no more than 50%, wherein LEN_(REST) represents a rest length ofthe fixation antenna along the longitudinal axis when in a restnon-extended state, and LEN_(EXTEND) represents an extended length ofthe fixation antenna along the longitudinal axis when deflected to afully extended state. The transceiver circuit and fixation areconfigured to communicate at a frequency of at least one of 400 MHz or2.4 GHz. The fixation antenna has a diameter between 2.5 mm and 5 mm.

In accordance with embodiments herein, a method for providing animplantable medical device, includes assembling a device housing havingelectronic circuits therein; connecting a feedthrough assembly to thedevice housing. An electrode connects to the feedthrough assembly. Afixation antenna connects to the feedthrough assembly, the fixationantenna being configured for operation as an antenna to communicate withan external device. The fixation antenna has a predetermined length totune the fixation antenna to a communication frequency.

Optionally, the method comprises tuning the fixation antenna tocommunicate in accordance with at least one of a MICS protocol,Bluetooth protocol, BLE protocol, or WiFi protocol. A length of thefixation antenna is set to be a multiple of a wavelength for a frequencyfor one of 400 MHz or 2.4 GHz. The fixation antenna is formed of amaterial having a deflection DEF=LEN_(REST)/LEN_(EXTEND) that is no morethan 50%, wherein LEN_(REST) represents a rest length of the fixationantenna along the longitudinal axis when in a rest non-extended state,and LEN_(EXTEND) represents an extended length of the fixation antennaalong the longitudinal axis when deflected to a fully extended state.

In accordance with an embodiment a leadless implantable medical deviceincludes a hermetic housing with a pacing electrode disposed on a distalportion of the housing. A fixation antenna is disposed on the distalportion of the housing. The fixation antenna is configured for operationas a monopole antenna to communicate with an external device. Anelectronics circuit is disposed in the housing and configured togenerate and deliver pacing signals to the pacing electrode. Afeedthrough assembly operatively connects the fixation antenna to theelectronic circuit.

Optionally, the fixation antenna includes a body that extends between aproximal end and the distal end, the body having a length defined basedon a wavelength of a carrier frequency for communication with theexternal device. The length of the body is a quarter multiple of thewavelength of the carrier frequency. The fixation antenna is shaped as ahelix with less than five turns of rotation from the distal end to theproximal end. The fixation antenna comprises less than five turns ofrotation from the distal end of the fixation antenna to the proximal endof the fixation antenna. The fixation antenna comprises less than oneand a quarter turns of rotation from the distal end of the fixationantenna to the proximal end of the fixation antenna. The fixationantenna has a body that is shaped as one of a helix, hook or straightneedle. The helix rotates less than or equal to 1800 degrees. Thehousing is elongated and extends along a longitudinal axis. The fixationantenna is wound in a helix about the longitudinal axis and is formed ofa material having a deflection DEF=LEN_(REST)/LEN_(EXTEND) that is nomore than 50%, wherein LEN_(REST) represents a rest length of thefixation antenna along the longitudinal axis when in a rest non-extendedstate, and LEN_(EXTEND) represents an extended length of the fixationantenna along the longitudinal axis when deflected to a fully extendedstate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a sectional view of a patient's heart with a leadlessimplantable medical device (LIMD) implanted therein.

FIG. 2 illustrates a side view of the LIMD and a schematicrepresentation of internal components according to an embodiment.

FIG. 3 illustrates an enlarged side view of a distal end of the LIMDpacemaker according to an embodiment.

FIG. 4 illustrates an enlarged perspective view of the distal end of theLIMD according to an embodiment.

FIG. 5 illustrates a partial cross-section view of the LIMD according toan embodiment.

FIG. 6 illustrates a method for providing the LIMD according to anembodiment.

DETAILED DESCRIPTION

The foregoing summary, as well as the following detailed description ofcertain embodiments, will be better understood when read in conjunctionwith the appended drawings. To the extent that the figures illustratediagrams of the functional blocks of various embodiments, the functionalblocks are not necessarily indicative of the division between hardwareand circuitry. Thus, for example, one or more of the functional blocks(e.g., processors or memories) may be implemented in a single piece ofhardware (e.g., a general purpose signal processor or a block or randomaccess memory, hard disk, or the like). Similarly, the programs may bestandalone programs, may be incorporated as subroutines in an operatingsystem, may be functions in an installed imaging software package, andthe like. It should be understood that the various embodiments are notlimited to the arrangements and instrumentality shown in the drawings.

Embodiments may be implemented in connection with one or more leadlessimplantable medical devices (LIMDs). For example, the LIMD may representa cardiac monitoring device, pacemaker, cardioverter, cardiac rhythmmanagement device, defibrillator, neurostimulator, leadless monitoringdevice, leadless pacemaker and the like. Additionally or alternatively,the LIMD may include one or more structural and/or functional aspects ofthe device(s) described in U.S. Pat. No. 9,216,285 “Leadless ImplantableMedical Device Having Removable And Fixed Components” and U.S. Pat. No.8,831,747 “Leadless Neurostimulation Device And Method Including TheSame”, which are hereby incorporated by reference. Additionally oralternatively, the LIMD may include one or more structural and/orfunctional aspects of the device(s) described in U.S. Pat. No. 9,232,485“System And Method For Selectively Communicating With An ImplantableMedical Device”, which are hereby incorporated by reference.

As used herein, the term “LEN_(REST)” represents a rest unloaded lengthof a fixation antenna as measured along a longitudinal axis when in anoriginal unloaded state with no load applied to the fixation antenna.

The term “LEN_(EXTEND)” represents an extended length of the fixationantenna along the longitudinal axis when the fixation antenna isstretched or otherwise deflected to a fully extended state. The fullyextended state represents a state of the fixation antenna from which thefixation antenna will return approximately to the rest length when anextension force is released. For example, an extending force may beapplied to the fixation antenna to stretch the fixation antenna alongthe longitudinal axis until reaching the extended length whichcorresponds to an endurance limit. If the fixation antenna is stretchedbeyond the endurance limit, elastic properties of the fixation antennaare exceeded which will prevent the fixation antenna from returning toan original unloaded length once the load is released.

The term “leadless” generally refers to an absence ofelectrically-conductive leads that traverse vessels or other anatomyoutside of the intra-cardiac space, while “intra-cardiac” meansgenerally, entirely within the heart and associated vessels, such as thesuperior vena cava (SVC), inferior vena cava (IVC), coronary sinus (CS),coronary veins (CV), pulmonary arteries, and the like.

FIG. 1 illustrates a sectional view of a patient's heart 10 and shows aleadless implantable medical device (LIMD) 100, such as pacemaker, acardiac resynchronization device, a cardioverter, a defibrillator, orthe like. The LIMD 100 has been placed through the superior vena cava 12into the right atrium 14 of the heart 10. FIG. 1 also shows the inferiorvena cava 16, the left atrium 18, the right ventricle 20, the leftventricle 22, the atrial septum 24 that divides the two atria 14, 18,and a tricuspid valve 26 between the right atrium 14 and the rightventricle 20.

The LIMD 100 comprises a housing 102 configured to be implanted entirelywithin a single local chamber of the heart 10, such as entirely andsolely within the right atrium 14 or the right ventricle 20. Optionally,the LIMD 100 may be implanted entirely and solely within the left atrium18 or the left ventricle 22, which may require modified implant methodscompared to implantation in the right atrium 14 or the right ventricle20.

As shown in FIG. 1, a local chamber in which the LIMD 100 is implantedis the right ventricle 20. For example, the LIMD 100 is mounted orfixated to the tissue wall of the right ventricle 20 along the septum 24that divides the right ventricle 20 from the left ventricle 22. Theseptum 24 wall tissue in the right ventricle 20 may behavephysiologically differently than the non-septum ventricular wall tissue.An electrode on the LIMD 100 engages tissue that is part of theconductive network of the right ventricle 20. Optionally, the LIMD 100is implanted in an area near different regions of tissue that follow theconductive pattern of different chambers of the heart. The LIMD 100 mayhave another electrode that engages tissue that is part of theconductive network of another chamber, such as the right atrium 14. Inother embodiments, the LIMD 100 may be implanted at a different locationwithin the right ventricle 14 or within a different intra-cardiacchamber. Alternatively, multiple LIMDs may be implanted into thepatient's heart 10 within different chambers or different segments ofthe same chamber.

FIG. 2 illustrates a side view of the LIMD 100 and a schematicrepresentation of a portion of the internal components according to anembodiment. The LIMD 100 includes a hermetic housing 102 that iselongated and extends along a longitudinal axis 104. The housing 102 cancomprise a conductive, biocompatible, inert, and anodically safematerial such as titanium, 316L stainless steel, or other similarmaterials. In alternate embodiments, the housing 102 can becylindrically shaped, rectangular, spherical, or any other appropriateshapes. The housing 102 includes a proximate portion 106 and oppositedistal portion 108 configured for mounting to tissue of an intra-cardiacwall within a chamber of the heart 10 with a fixation antenna 110, andan intermediate portion 112 extending between the proximate portion 106and the distal portion 108.

The intermediate portion 112 includes a compartment 114 that containsthe electronics circuit 101 for operation of the LIMD 100, including,for example, a power supply 116, a memory 118, one or more processors120, a pulse generator 122, a sensing circuit 124, and a transceivercircuit 125. The electronics circuit 101 is configured to perform one orboth of sensing and stimulation operations. The electronics circuit 101may sense cardiac signals from one or more electrodes 126, such as inconnection with monitoring cardiac activity and/or sensing cardiacsignals to determine whether/when to deliver a pacing therapy. Theelectronics circuit 101 may also generate and deliver pacing signals toone or more electrodes 126.

More specifically, the sensing circuit 124 senses the cardiac signals,the processor 120 determines whether a pacing signal is warranted and ifso, the pulse generator 122 generates and delivers the pacing signal tothe electrode 126.

The transceiver (Tx/Rx) circuit 125 is configured to communicatewirelessly with an external device in accordance with a select protocol,such as a Bluetooth protocol, WiFi protocol, Bluetooth low energy (BLE)protocol, Medical Implant Communications Standard (MICS) protocol, andthe like.

In accordance with embodiments herein, the transceiver circuit 125 iselectrically coupled to the fixation mechanism 110 and the fixationmechanism 110 is configured to operate as an antenna for communicationbetween the LIMD 100 and an external device.

FIGS. 3-4 illustrate an enlarged side and top views of the distalportion 108 of the LIMD 100 according to an embodiment. A pacingelectrode 126 is disposed on the distal portion 108 of the housing 102with an insulative cap 128. The cap 128 electrically insulates thepacing electrode 126 from the proximate portion 106 of the housing 102.All or a portion of the proximate portion 106 of the housing 102 may beutilized as a separate electrode. Optionally, the LIMD 100 may includemultiple sensing/pacing electrodes positioned at select points about thehousing 102 (not shown). The electrodes may be located in variouslocations on the housing 102 based on the shape of the LIMD 100, theimplant location, the intended use of the LIMD 100 and the like. Forexample, when separate housing portions are provided for the electroniccomponents and the battery, one or more electrodes may be located on thehousing portion that holds the battery. An insulative coating may beprovided on a portion of the housing 102, such as between electrodes andcan comprise materials such as PEEK, tecothane, silicone, polyurethane,parylene, or another biocompatible electrical insulator commonly usedfor implantable medical devices. In some embodiments, the housing 102itself can comprise an insulator instead of a conductor, such as analumina ceramic or other similar materials, and electrodes can bedisposed upon the housing 102.

The pacing electrode 126 is configured for delivery of stimulationenergy to a tissue of interest. As used herein, “tissue of interest”refers to intra-cardiac tissue that the LIMD 100 is configured tomonitor and provide stimulation energy. In the illustrated embodiment,the LIMD 100 is configured for affixation directly to the tissue ofinterest, as described below. The pacing electrode 126 may be a cathodeelectrode that is actively fixated to the myocardium. The stimulationenergy may be in the form of low-energy pacing pulses, higher-energyshocking pulses, or the like. When the distal portion 108 is mounted tothe intra-cardiac tissue, the pacing electrode 126 is securely affixedto and engages the tissue of interest in order to deliver thestimulation energy directly thereto. In addition to deliveringstimulation energy, in an alternative embodiment the pacing electrode126 may be used to sense electrical activity from the tissue ofinterest. The pacing electrode 126 may be formed as a single conductivebulb or, alternatively, as a cone, a single wire, or the like.

The pacing electrode 126 can comprise a “button” or dome shape thatprotrudes slightly distally from the distal portion 108 of the LIMD 100.The dome shaped pacing electrode 126 can include a diameter of about1.5-2.5 mm and can protrude distally from the end of the pacemakerapproximately 0.05″ to 0.3″. The pacing electrode 126 is preferably anatraumatic surface, and can protrude from the distal portion 108 of theLIMD 100 to contact the tissue when the fixation antenna 110 is screwedinto tissue.

The fixation antenna 110 includes a body 111 that extends between adistal end 144 and a proximal end 146. The fixation antenna 110 cancomprise a helix that partially surrounds or rotates about thelongitudinal axis 104 and the cap 128. The helix can comprise a constantdiameter that is less than or equal to the outer diameter of thepacemaker housing 102. In one embodiment, the fixation antenna 110comprises a diameter of less than 5 mm. In another embodiment, thefixation antenna 110 comprises a diameter of greater than 2.5 mm andless than 5 mm. In some embodiments, the helical fixation antenna 110can have a wire diameter of 0.005″ to 0.03″ and a pitch of 0.5 mm to 1.5mm. Each coil of the fixation antenna 110 includes a gap G that is largeenough to prohibit contact and electrical shorts between the coils.Utilizing a fixation antenna 110 having a diameter up to the diameter ofthe housing 102 can increase the pull force required to remove thefixation antenna 110 from tissue, thereby decreasing the chances of thedevice coming dislodged from the heart 10. Furthermore, the increaseddiameter of the fixation antenna 110 can increase the surface area incontact with the endocardium layer of the heart 10, further improvingthe ability of the LIMD 100 to remain implanted in the patient.

The helical fixation antenna 110 can comprise a coil having less thanfive (5) full rotations from the distal end 144 of the fixation antenna110 to the proximal end 146. For example, the distal end 144 of thefixation antenna 110 is approximately three (approximately 1,080degrees) from the proximal end 116 of the fixation antenna 110. The cap128 and fixation antenna 110 can have an outer diameter less than theouter diameter of the intermediate portion 112 and proximate portion 106of the housing 102, so as to facilitate attachment of the fixationantenna 110. When the fixation antenna 110 is fully screwed into thecardiac tissue, the pacing electrode 126 of the LIMD 100 is in solidcontact with the tissue.

Optionally, the fixation antenna 110 can include anti-rotation features148 such as barbs or sutures to prevent counter rotation of the deviceonce it has been screwed into tissue.

The helical fixation antenna 110, can enable insertion of the deviceendocardially or epicardially through a guiding catheter. A torqueablecatheter can be used to rotate the housing 102 and force the fixationantenna 110 into heart tissue, thus affixing the fixation antenna 110(and also the pacing electrode 126 in FIG. 1) into contact withstimulable tissue. The fixation antenna 110 may be coated partially orin full for electrical insulation, and a steroid-eluting matrix may beincluded on or near the device to minimize fibrotic reaction, as isknown in conventional pacing electrode-leads.

The fixation antenna 110 operates as a monopole antenna. For example,the fixation antenna 110 may be formed as a wire antenna connected atthe proximal end 146 to the feedthrough pin 134 and open at the distalend 144. RF signals are conducted from the transceiver circuit 125through the feedthrough assembly 130, along the fixation antenna 110,toward the open distal end 144 where the signal radiates into space.

The length of the fixation antenna 110 is adjusted to tune the antennacharacteristics to a desired frequency. The length of the fixationantenna 110 is directly related to a resonant frequency of operation,and thus the length can be adjusted to be longer or shorter depending onthe communications protocol being used. For example, in certainapplications, the fixation antenna 110 may be tuned to communicate at aselect frequency of 400 MHz or 2.4 GHz. The fixation antenna 110 may beconstructed to support communications in the frequency ranges associatedwith a Bluetooth protocol, a Wi-Fi protocol, Medical ImplantCommunications Standard (MICS), or various other wireless protocols.

As a further example, the body 111 of the fixation antenna 110 may beformed with a length based on a wavelength of a carrier frequency withan external device, such as a length that corresponds approximately to(or is greater than) a quarter multiple of the wavelength of the desiredcarrier frequency. For example, when the fixation antenna operates atthe frequency of 2.4 GHz, the fixation antenna may be constructed withan overall length of approximately 31.25 mm. Optionally, the fixationantenna may be constructed to have a length corresponding to or greaterthan one half of the wavelength of the desired frequency. As a furtherexample, the fixation antenna 110 may have a length that is equal to orgreater than the wavelength of the desired frequency. For example, whenutilizing the frequency of 2.4 GHz, the overall length may beapproximately 62.5 mm, 93.75 mm, 125 mm, etc. The overall length of thefixation antenna 110 is measured from the distal end 144 to the proximalend 146. The pitch and the height of the helix can also vary toaccommodate communication requirements or standards. In addition, theinsertion of a portion of the fixation antenna 110 in heart tissue helpsmaintain the impedance generally constant. Generally, antenna impedanceis more stable when the antenna is inserted into heart tissue as opposedto blood. For example, there is less movement of the antenna whenanchored into heart tissue. As a result, the antenna maintains aconstant contact with the heart tissue. In addition, heart tissue hasknown and generally consistent material properties. In contrast, thematerial properties of blood can vary.

The fixation antenna 110 comprises a generally rigid material with lowdeflection characteristics, such as a shore hardness ranging between35-55 Rockwell C HRC. For example, the fixation antenna 110 can beformed of a material having a deflection DEF=LEN_(REST)/LEN_(EXTEND)that is no more than 50%, wherein LEN_(REST), and LEN_(EXTEND) aredescribed above in the terms section. The deflection of the fixationantenna 110 from the initial to final length is typically no more than50%, and preferable 5%-40%.

LIMD Circuits

FIG. 5 illustrates a partial cross-section view of the LIMD 100according to an embodiment. The housing 102 includes a cap 128 that ismounted to a feedthrough assembly 130. The pacing electrode 126 isprovided on the cap 128. The pacing electrode 126 is electricallyconnected to the electronics circuits 101. The electronics circuits 101is mounted to one or more circuit boards 132 that are coupled tofeedthrough pins 134 at pads 136. The feedthrough pins 134 extendthrough the feedthrough assembly 130 and are electrically coupled withthe pacing electrode 126 and fixation antenna 110 through respectivewires 138, 139 and suitable connection, such as welding, soldering, orconnector, with feedthrough pins 134. The feedthrough pins 134 mayinclude a dielectric material (not shown) that separates the inner andouter portions of the pins 134. Conductors 140 connect to the circuitboard 132 with pads 142 and electrically connect to the power supply116, such as a battery. Optionally, a ground connection (not shown) canalso be maintained between the feedthrough assembly 130 and the circuitboard 132. It is understood that the example of FIG. 5 represents oneexemplary construction, while LIMDs may be constructed with numerousalternative shapes and combinations of components therein.

As mentioned above, the housing 102 includes a power supply 116 andvarious electronics circuits 101 that receive electrical current fromthe power supply 116. The electronics circuits 101 provide thefunctionality of the LIMD 100, such as controlling the stimulationenergy delivered to the pacing electrode 126 and sensing thedepolarization along the tissue of interest in response to a pacingpulse or to an intrinsic heartbeat. The power supply 116 may be abattery that has a fixed amount of charge at full capacity. The powersupply 116 may be rechargeable in some embodiments, and may not berechargeable in other embodiments.

The illustration in FIG. 2 is intended as an overview of the electroniccomponents only, and the electronic components according to anembodiment of the LIMD 100 are described in more detail below withreference to FIG. 5. The pulse generator 122 provides stimulation energyto the pacing electrode 126 which is delivered to the tissue of interestthat the pacing electrode 126 engages. The pulse generator 122 includescircuitry to control the output of stimulation energy directed to thepacing electrode 126. For example, the pulse generator 122 produceslower energy pulses for pacing and higher energy pulses for shocking.

The processor 120 is a controller that controls the flow of chargebetween the power supply 116, the electronics circuits 101 (such as thepulse generator 122 and the sensing circuit 124), and the electrodes(such as pacing electrode 126). For example, the processor 120 controlsthe timing and intensity or magnitude of the stimulation pulses. Ifmultiple electrodes are used to deliver stimulation energy to theintra-cardiac tissue, the processor 120 may synchronize the delivery ofthe pulses. The processor 120 is communicatively coupled to the pulsegenerator 122, the sensing circuit 124, the memory 118, and the powersupply 116. The processor 120 controls the flow of charge based on inputinformation received from the sensing circuit 124. The processor 120also functions based on instructions stored locally in the memory 118.The memory 118 is a non-transitory tangible computer readable storagemedium. The memory 118 stores programmable and executable instructionsfor the processor 120. The processor 120 is responsive to theprogrammable instructions to control operation of the LIMD 100. Thememory 118 may also store data. Some of the data may be stored prior tocompleting assembly of the LIMD 100, while other data may be storedduring use of the implanted LIMD 100. For example, the memory 118 may beused to store data on intrinsic electrical activity within the heart asmonitored by the sensing circuit 124, data on the number, time, and/ormagnitude of pacing pulses generated by the pulse generator 122, or thelike.

The sensing circuit 124 is configured to monitor intrinsic electricalactivity within the heart. The sensing circuit 124 is communicativelycoupled to the pacing electrode 126 which doubles as a sensingelectrode, such that the pacing electrode 126 is used to deliverstimulation pulses and, in-between pulses, monitors the electricalactivity within the tissue of interest for the sensing circuit 124. Inan alternative embodiment, the sensing electrode is different from thepacing electrode 126, because the sensing electrode does not deliverstimulation energy to the intra-cardiac tissue.

FIG. 6 illustrates a method for providing an implantable cardiacmonitoring device in accordance with embodiments herein. At 602, theprocess includes assembling a device housing having electroniccomponents therein. Examples of the various electronic components aredescribed herein. The electronic components may include sensingcircuitry to sense cardiac signals of interest, one or more processorsto perform monitoring operations, transceiver circuitry to communicatewith external devices and other components as described herein and/orunderstood by one of ordinary skill in the art. The memory, processors,and other electronic components are within a housing formed of abiocompatible material.

At 604, the process includes connecting a feedthrough assembly to thedevice housing. The housing includes a feedthrough opening at one endand a battery attachment at the opposite end. A hermetically sealedbattery is welded to the battery attachment surface, and a feedthroughis welded to the feedthrough opening, thereby hermetically sealing theinterior of the housing.

At 606 a pacing electrode includes connecting a pacing electrode to thefeedthrough assembly. The pacing electrode 126 is configured fordelivery of stimulation energy to a tissue of interest.

At 608, a fixation antenna is connected to the feedthrough assembly toelectrical components. The fixation antenna operates as a monopoleantenna for communication with external devices. The fixation antennacan have a predetermined configuration, such as a predetermined length,pitch, and shape to tune the antenna to a communications frequency orstandard. The fixation antenna includes an overall length extending froma proximal end that is connected to feedthrough pins of the feedthroughassembly, to an open distal end, for communication of RF signals.

It should be clearly understood that the various arrangements andprocesses broadly described and illustrated with respect to the Figures,and/or one or more individual components or elements of sucharrangements and/or one or more process operations associated of suchprocesses, can be employed independently from or together with one ormore other components, elements and/or process operations described andillustrated herein. Accordingly, while various arrangements andprocesses are broadly contemplated, described and illustrated herein, itshould be understood that they are provided merely in illustrative andnon-restrictive fashion, and furthermore can be regarded as but mereexamples of possible working environments in which one or morearrangements or processes may function or operate.

The processors/applications herein may include any processor-based ormicroprocessor-based system including systems using microcontrollers,reduced instruction set computers (RISC), application specificintegrated circuits (ASICs), field-programmable gate arrays (FPGAs),logic circuits, and any other circuit or processor capable of executingthe functions described herein. Additionally or alternatively, theprocessors/controllers herein may represent circuit modules that may beimplemented as hardware with associated instructions (for example,software stored on a tangible and non-transitory computer readablestorage medium, such as a computer hard drive, ROM, RAM, or the like)that perform the operations described herein. The above examples areexemplary only, and are thus not intended to limit in any way thedefinition and/or meaning of the term “controller.” Theprocessors/applications herein may execute a set of instructions thatare stored in one or more storage elements, in order to process data.The storage elements may also store data or other information as desiredor needed. The storage element may be in the form of an informationsource or a physical memory element within the processors/controllersherein. The set of instructions may include various commands thatinstruct the processors/applications herein to perform specificoperations such as the methods and processes of the various embodimentsof the subject matter described herein. The set of instructions may bein the form of a software program. The software may be in various formssuch as system software or application software. Further, the softwaremay be in the form of a collection of separate programs or modules, aprogram module within a larger program or a portion of a program module.The software also may include modular programming in the form ofobject-oriented programming. The processing of input data by theprocessing machine may be in response to user commands, or in responseto results of previous processing, or in response to a request made byanother processing machine.

It is to be understood that the subject matter described herein is notlimited in its application to the details of construction and thearrangement of components set forth in the description herein orillustrated in the drawings hereof. The subject matter described hereinis capable of other embodiments and of being practiced or of beingcarried out in various ways. Also, it is to be understood that thephraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having” and variations thereof herein ismeant to encompass the items listed thereafter and equivalents thereofas well as additional items.

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, the above-describedembodiments (and/or aspects thereof) may be used in combination witheach other. In addition, many modifications may be made to adapt aparticular situation or material to the teachings herein withoutdeparting from its scope. While the dimensions, types of materials andcoatings described herein are intended to define various parameters,they are by no means limiting and are illustrative in nature. Many otherembodiments will be apparent to those of skill in the art upon reviewingthe above description. The scope of the embodiments should, therefore,be determined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled. In the appendedclaims, the terms “including” and “in which” are used as theplain-English equivalents of the respective terms “comprising” and“wherein.” Moreover, in the following claims, the terms “first,”“second,” and “third,” etc. are used merely as labels, and are notintended to impose numerical requirements on their objects or order ofexecution on their acts.

What is claimed is:
 1. A method for providing an implantable medicaldevice, comprising: providing a device housing having electroniccircuits therein; disposing an electrode on the housing; and disposing afixation antenna on a distal end of the housing, the fixation antennabeing configured for operation as an antenna to communicate with anexternal device,wherein the fixation antenna has a predetermined lengthto tune the fixation antenna to a communication frequency.
 2. The methodof claim 1, further comprising: connecting a feedthrough assembly to thedevice housing; connecting the electrode to the feedthrough assembly;and connecting the fixation antenna to the feedthrough assembly.
 3. Themethod of claim 1, wherein the electrode is disposed on a distal portionof the housing.
 4. The method of claim 1, further comprising tuning thefixation antenna to communicate in accordance with at least one of aMICS protocol, Bluetooth protocol, BLE protocol, or WiFi protocol. 5.The method of claim 1, further comprising setting a length of thefixation antenna to be a multiple of a wavelength for a frequency forone of 400MHz or 2.4 GHz.
 6. The method of claim 1, further comprisingforming the fixation antenna of a material having a deflectionDEF=LEN_(REST)/LEN_(EXTEND) that is no more than 50%, wherein LEN_(REST)represents a rest length of the fixation antenna along the longitudinalaxis when in a rest non-extended state, and LEN_(EXTEND) represents anextended length of the fixation antenna along the longitudinal axis whendeflected to a fully extended state.
 7. The method of claim 1, whereinthe fixation antenna is electrically separate from the electrode andpartially disposed on a distal portion of the housing, the fixationantenna being configured to penetrate cardiac tissue to affix theleadless implantable device to the cardiac tissue, the fixation antennabeing electrically coupled to a transceiver circuit and configured tooperate as an antenna for communication between the transceiver circuitand the external device.
 8. The method of claim 7, wherein: the housingincludes a feedthrough, the fixation antenna including a proximal endconnected through the feedthrough to the transceiver circuit, and thefixation antenna including a distal end that is electrically open. 9.The method of claim 1, wherein the fixation antenna is configured tooperate as a monopole antenna for communication between the transceivercircuit and the external device.
 10. The method of claim 1, wherein thefixation antenna includes a body that extends between the proximal anddistal ends, the body having a length defined based on a wavelength of acarrier frequency for communication with the external device.
 11. Themethod of claim 10, wherein the length of the body is a quarter multipleof the wavelength of the carrier frequency.
 12. The method of claim 1,further comprising shaping a body of the fixation antenna as one of ahelix, hook or straight needle.
 13. The method of claim 1 wherein thefixation antenna has a diameter between 2.5 mm and 5 mm.
 14. A leadlessimplantable medical device, comprising: a housing; a pacing electrodedisposed on a distal portion of the housing; a fixation antenna disposedon a distal end of the housing, the fixation antenna configured foroperation as a monopole antenna to communicate with an external device;and an electronics circuit disposed in the housing, the electronicscircuit configured to generate and deliver pacing signals to the pacingelectrode.
 15. The leadless implantable medical device of claim 14,further comprising a feedthrough assembly operatively connecting thefixation antenna to the electronic circuit.
 16. The leadless implantablemedical device of claim 14, wherein the fixation antenna includes a bodythat extends between a proximal end and the distal end, the body havinga length defined based on a wavelength of a carrier frequency forcommunication with the external device.
 17. The leadless implantablemedical device of claim 16, wherein the length of the body is a quartermultiple of the wavelength of the carrier frequency.
 18. The leadlessimplantable medical device of claim 16, wherein the fixation antenna isshaped as a helix with less than five turns of rotation from the distalend to the proximal end.
 19. The leadless implantable medical device ofclaim 16, wherein the fixation antenna comprises less than one and aquarter turns of rotation from the distal end of the fixation antenna tothe proximal end of the fixation antenna.
 20. The leadless implantablemedical device of claim 14, wherein the fixation antenna has a body thatis shaped as one of a helix, hook or straight needle.